1. Field of Invention
The present invention relates to a cholesteric liquid crystal color filter plate which is formed of cholesteric liquid crystal.
2. Discussion of Related Art
When a cholesteric liquid crystal (hereinafter abbreviated CLC) is irradiated with a light ray consisting of various wavelengths, such as white light, most of the optically active light is transmitted through the liquid crystal with the exception of light having a wavelength which approximates the pitch of the liquid crystal. Namely, a CLC will selectively reflect light having a wavelength region equivalent to the intrinsic pitch of cholesteric phase. For this reason, a CLC shows a color within the visible light region owing to its pitch. Thus, by using such characteristics, a CLC can be used for a color filter or a color polarizer.
FIG. 1 shows the permeability of cholesteric liquid crystals having homogeneous pitches reflecting blue, green, and red lights of a visible light ray, respectively, in accordance with their wavelengths. Referring to FIG. 1, xe2x80x9cliquid crystal Ixe2x80x9d designates a CLC selectively reflecting blue light in the range of approximately 430-500 nm, xe2x80x9cliquid crystal IIxe2x80x9d selectively reflects a green light in the range of approximately 520-570 nm, and xe2x80x9cliquid crystal IIIxe2x80x9d selectively reflects red light in the range of approximately 580-660 nm.
CLCs may be divided into two categories, thermochromic and monochromic, in accordance with the possibility of controlling the pitch depending on fabrication temperatures.
A thermochromic CLC has a pitch which can be controlled according to its hardening temperature, thus enabling the selection of a specific light wavelength region for reflection. On the other hand, a monochromic CLC has a single characteristic pitch and only reflects a single preselected light wavelength.
FIG. 2A to FIG. 2C show schematic cross-sectional views of fabricating a color filter using thermochromic CLCs for explaining one type of the related art.
Referring to FIG. 2A, a top of a substrate 200 is coated with a first thermochromic CLC layer 21. Then, a predetermined portion of the first thermochromic CLC layer 21 is hardened by selective exposure through a photomask M at a first process temperature. In this case, the exposed portion of the first thermochromic CLC layer 21 is hardened to have a first pitch under the first temperature, thereby becoming a first light wavelength region, for example, a region R enabling the reflection of red light only.
Referring to FIG. 2B, a green region G is formed at the other portion of the first thermochromic CLC layer 21 by the same method used for forming the red region R. Namely, the remaining portion of the first thermochromic CLC layer 21 is hardened by another selective exposure through the photomask M at a second process temperature. In this case, the exposed portion of the first thermochromic CLC layer 21 is hardened to have a second pitch under the second temperature, becoming a second light wavelength region, for example, a green region G enabled to reflect only green light wavelengths.
Referring to FIG. 2C, a second thermochromic CLC layer 22 in which a blue region B and a red region R are arranged is formed on the first thermochromic CLC layer 21 where the red region R and green region G have been arranged in order. The red and blue regions R and B are formed by the above mentioned method.
In this case, each of the regions in the second thermochromic CLC layer 22 is formed not to overlap with the same kind of region of the first thermochromic CLC layer 21. A ray permeating through the area where the red and green regions R and G overlap one another, of which red and green lights are reflected thereon and a blue light passes through, realizes a blue color. By the same principle, as shown in FIG. 2C, green light and red light pass through, realizing a green color and a red color, respectively.
FIGS. 3A and 3B show schematic cross-sectional views of fabricating a color filter using monochromic CLCs according to a second related art.
A monochromic CLC has a characteristic pitch of the cholesteric phase, and a color filter is fabricated by the same process as the conventional fabrication of color filters.
Referring to FIG. 3A, a top surface of a substrate 300 is coated with a monochromic CLC layer which reflects a first light wavelength region such as a red light. The monochromic CLC layer is selectively exposed and developed, forming a red region R. Then, a green region G is formed by forming another monochromic CLC layer reflecting a second wavelength zone such as a green light, followed by selective exposure and development. A blue region B is also formed by the same method.
Thus, the red, blue and green regions R, B, and G are located in a first layer.
Referring to FIG. 3B, red blue and green regions R, B, and G of a second layer are formed on the red blue and green regions R, B, and G located at the first layer by carrying out the same process mentioned in the above description. In this case, each of the regions in the second layer is formed not to overlap with the same kind region of the first layer.
As a result, a color filter permeable only to a predetermined color is fabricated.
A drawback of the above described related art technology is that the formation of the respective regions by using a thermochromic CLC having a predetermined pitch requires the control of exposure and temperature whenever the respective regions are to be formed. As a result, this technology requires more process equipment and is time consuming.
Disadvantages from the related art technologies arise from the stacking of the multiple layers required to manufacture a filter. Misalignment of the liquid crystals can cause light scattering at the interface between the layers. The stacking of layers also results in a thick color filter having a tendency to degrade. A multilayered filter requires additional manufacturing steps result in higher manufacturing costs and an increased reject rate.
The invention is directed to fabricating a semiconductor device that substantially eliminates one or more of the problems due to the limitations and disadvantages of the related art.
A cholesteric liquid crystal color filter plate is formed from a single CLC layer by using a mixture of liquid crystal and dye. The filter plate is manufactured by mixing a cholesteric liquid crystal reflecting one specific color wavelength zone with a dye absorbing another specific light wavelength zone. The filter plate can also be made by using a liquid crystal mixture reflecting at least two continuous light wavelength zones.
The filter plate includes, in part, a substrate. On the substrate is formed a first light filter region formed of a cholesteric liquid crystal mixture is permeable by a red wavelength zone by reflecting blue and green wavelength zones. A second light filter region on the substrate is formed of a cholesteric liquid crystal mixture permeable to the blue wavelength zone by reflecting the green and red wavelength zones. A third light filter region on the substrate is formed of a cholesteric liquid crystal-dye mixture permeable to the green wavelength zone. The cholesteric liquid crystal-dye mixture of the third filter region is manufactured by mixing a cholesteric liquid crystal reflecting one of the red wavelength zone and the blue wavelength zone with a dye absorbing the remaining wavelength zone which is not selected by the cholesteric liquid crystal. The first, second and third light filter regions lie continuously on the substrate and form a single layer.
In another embodiment, the filter can include a substrate, and a first to third light filter regions on the substrate. The first to third light filter regions are permeable to different light wavelength zones, i.e., red, green and blue, respectively. The first to third light filter regions are formed by mixing a cholesteric liquid crystal selectively reflecting one of red, green, and blue wavelength zones with a dye absorbing one of the remaining wavelength zones not reflected by the cholesteric liquid crystal. As a result, each cholesteric liquid crystal-dye mixture has the characteristic of being permeable to the remaining wavelength zone which is selected by neither the cholesteric liquid crystal nor the dye. The first, second and third light filter regions lie continuously on the substrate and form a single layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.